grep a url on a specific line

I'm grepping spam from my application logs.

I'm looking for the one line URL spam.  It will always show up on my third line

---------
blah
blah
http://spam.com/url.html
----------

How do I grep only the third line and how to I grep to see if a URL exists?

md168Asked:
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md168Author Commented:
I figured out how to find the specific line: head -3 spam.txt | tail -1

Now, I need to search for a URL
wesly_chenCommented:
#!/bin/sh

LOG_FILE=/path-to-application-log

STRING=`head -3 $LOG_FILE | tail -1`
if [ "$STRING" =~ "http" ]
then
   echo $STRING
fi

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farzanjCommented:
Try this one

sed -n 3p spam.txt | grep http

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farzanjCommented:
Or try this one even simpler and more efficient
sed -n  3,/http/p

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md168Author Commented:
I couldn't get the sed to work.  I'll use the wesly's script.  Thanks.
farzanjCommented:
Both the sed work

What is the error message
wesly_chenCommented:
Hi farzanj, I believe your second one is
sed -n 3,/http/p spam.txt
farzanjCommented:
Hi Wesly,
Yes, I forgot the file name but the first one worked too.  It had filename as well.  And both DO work.
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